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68                         METALLURGY   OF   CAST   IRON.                                              !
simply by having a hole in the lining through to the inside of the furnace, and after the same is tapped to plug it with clay, on the same principle generally followed in tapping a slag-hole in cupola work. The modern plan for making and operating a flushing-hole is that shown in Figs. 18 and 19, pages 90 and 93. At            i
N is a bronze casting into which is inserted what is termed a " monkey tuyere," P, both of which are kept cool by a flow of water passing through them. In tapping a slag-hole to flush a furnace the projection H is slightly jarred by means of a sledge which loosens the stopper R. After this has been removed, as shown by A, Fig. 18, a steel pointed bar is then used to cut through the inch or two of chilled slag, which has generally been formed in front of the plug F. This chilled slag is generally removed with ease, permitting the cinder to flow out. The time generally taken for the slag to be all flushed out ranges from five to seven minutes. It is not long after the slag has commenced to run before the blast makes its appearance, blowing gas and sparks of cinder for from twenty to thirty feet from the flushing-hole. As soon as the flushing is completed, the iron plug stopper R is quickly thrust into the hole, which at once chills the slag around it, and stops the leakage of blast. The stopper R is a wrought iron bar with a cast iron cone cast on the rod which forms the plug as shown. The difference between this method of tapping a flushing-hole and the old plan used is simply in the convenience, and the use of clay is avoided. The iron and slag-holes of a furnace are sometimes lowered or raised from their original positions by reason of a furnace filling up with chilled iron, but if this can be avoided by tapping the
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